Gate Turn-Off Thyristor
M.S.P.V.L Polytechnic College,
Pavoorchatram.
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Introduction
 A Gate Turn-Off Thyristor (GTO) is a special type of thyristor, a
high-power semiconductor device.
 GTOs, as opposed to normal thyristor, are fully controllable switches
which can be turned on and off by their third lead, the GATE lead.
 GTO thyristor can be fabricated with a reverse conducting diode in the
same package. These are known as RCGTO, for Reverse Conducting
GTO.
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Circuit diagram of GTO
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GTO Diagram and Symbol
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Reverse BIAS
 GTO thyristor are available with or without reverse blocking
capability.
 Reverse blocking capability adds to the forward voltage drop
because of the need to have a long, low doped P1 region.
 GTO thyristor capable of blocking reverse voltage are known
as Symmetrical GTO thyristor, abbreviated S-GTO
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Functions of GTO
 Gate turn-off thyristor (GTOs) are four-layer PNPN devices that act
as switches, rectifiers, and voltage regulators.
 Like other thyristor, GTOs can be turned on by the application of a
positive gate signal (g > 0); however, unlike other more conventional
devices that can be turned off only at a zero crossing of current,
GTOs can be turned off at any time by the application of a gate
signal equal to zero.
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Functions of GTO
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Functions of GTO
 Performance specifications for gate turn-off thyristor (GTOs) include
peak repetitive off-state voltage, peak repetitive reverse voltage,
peak cycle surge-on current, maximum root mean square (RMS)
current, and holding current.
 Peak repetitive off-state voltage (VDRM) is the maximum
instantaneous value of the off state.
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Cross section of GTO
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Operations of GTO
 When a positive signal is applied, a GTO switches into conduction
state like the ordinary thyristor.
 However in ordinary thyristor the current gains of NPN and PNP
transistors are very high so that gate sensitivity for turn on is very high
and on state voltage drop is low.
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Structure of GTO
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Operations of GTO
 However in GTO, the current gain of PNP transistor is low so that
turn of its possible if significant current is drawn from the gate.
 When a negative gate signal is applied the excess carriers are drawn
from the base region of NPN transistor and collector current of
PNP is diverted to the gate.
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Operations of GTO
 Thus the base drive of NPN transistor is removed and
this in turn removes the base drive of PNP transistor and
turnoff is achieved.
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The End
…… Thank You …….
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